Such a positive-displacement pump is known from DE-A1-41 01 210. The throttle orifice of the bypass flow control valve of this pump is arranged on a movable piston. Because of this, the flow control valve controls the positive-displacement pump with a dropping flow characteristic. This means that at an increasing number of revolutions the flow conveyed by the pump is governed. The reduced conveyed flow causes a reduced throughput pressure in the steering system and therefore a reduction of the power consumption.
In another known positive-displacement pump (DE-A1-44 33 598 or U.S. Pat. No. 5,810,565), a control throttle is displaced as a function of the conveyed flow. This means that the regulation takes place independently of the pressure. In this case, the adjustment signal is a pulse. Regulation as a function of the pressure is not possible.
However, with pumps of this type the effect of the reduced power consumption only occurs at increased numbers of revolutions.